The present invention relates generally to optical multiplexers/demultiplexers. More specifically, the present invention relates to zigzag pathway optical multiplexers/demultiplexers with discrete optical filters wherein adjacent filters on a common surface (typically a flat surface of a molded optical block) have an optically transparent region between filters. The present invention recognizes that said optically transparent regions create optical noise; that noise is reduced by applying a patterned opaque layer between filters.
The present invention is particularly effective in reducing optical noise in the multiplexer/demultiplexer design shown and described in U.S. application Ser. No. 09/347,490, which is incorporated by reference herein as though set forth in full. The present invention is also applicable to other optical multiplexer/demultiplexer designs which utilize two or more discrete filters on a common surface having an optically transparent region between those discrete filters.
Prior art optical multiplexers and demultiplexers include the Nosu et al U.S. Pat. No. 4,244,045. Nosu utilizes a series of wavelength sensitive filters arranged in a zigzag optical pathway at a predetermined oblique angle to the light beam. Nosu positions filters on both sides of substrate 60. It is significant that the fabrication of the Nosu device is expensive and time consuming. No suggestion is made in Nosu concerning reduction of optical noise or the use of an opaque layer between filters.
The Scobey U.S. Pat. Nos. 5,583,683 and 5,786,915 teach an eight channel multiplexing device in which a continuous variable thickness interference filter is deposited onto the surface of an optical block. This design has inherent weaknesses. First, each filter must necessarily integrate the signal over its width, since its thickness (and wavelength sensitivity) varies across its width; resulting in less precise filtering. Secondly, the interference filter thickness may vary from device to device, also degrading its filtering performance. Thirdly, each of the individual couplers such as item 62 of FIG. 3 must be separately aligned after fabrication. Fourth, no suggestion is made concerning the use of an opaque layer to reduce optical noise.
The Scobey et al U.S. Pat. No. 5,859,717 teaches the use of a precision optical block which is opaque (col. 4, lines 20-29) and in which slots or gaps are machined or formed to provide an optical path, resulting in an inherently very expensive product. Furthermore, the separate collimators (6,24,46) and filters 32 must be separately aligned after fabrication of the device, adding to the time and expense of production. The present invention utilizes a patterned opaque region applied to a molded optical block, which is much cheaper than machining an opaque material. The present invention avoids the separate alignment of filters required by Scobey""717.
The Jayaraman U.S. Pat. No. 5,835,517 teaches an optical multiplexer having multiple optical cavities which must each be xe2x80x9ctunedxe2x80x9d after fabrication by adjusting its length. No suggestion is made of using an opaque pattern to reduce optical noise.
The Lemoff et al U.S. Pat. No. 5,894,535 teaches an optical multiplexer in which a plurality of dielectric channel waveguides are embedded in a cladding region, which process is considerably more expensive than the monolithic formed optical blocks used in the present invention. Furthermore, the filters must be separately aligned with the channel waveguides after fabrication. No suggestion is made of using opaque regions between filters to reduce optical noise.
An optical multiplexing device combines or separates multiple light signals with varying optical frequencies. The optical multiplexing device has applications for both dense and coarse wavelength division multiplexing (DWDM and CWDM) for both multi-mode and signal-mode fiber optic data communications and telecommunications. Multiple wavelength light sources are combined into a single optical path for transmission or multi-wavelength light travelling in a single optical path is separated into multiple narrow spectral bands that is focused onto individual fiber optic carriers or detectors.
Current wavelength division multiplexed (WDM) devices are designed for operation in single-mode optical fiber telecommunications systems, where performance over long distances ( greater than 100 km) is the primary factor and cost and size are secondary. As bandwidth demands within the Networking Industry [Local Area Networks (LAN) and Wide Area Networks (WAN)] increase, compact inexpensive wavelength division multiplexed systems will become necessary in order to utilize the full bandwidth of the optical fiber. The WDM device described herein utilizes plastic-mold injection and inexpensive dielectric filters to create a compact device capable of multiplexing or demultiplexing multiple optical wavelengths.
A primary object of the invention is to provide a patterned opaque layer between adjacent, discrete filters in an optical multiplexer/demultiplexer in order to reduce optical noise.
Another object of the present invention is to provide a compact and cost effective optical multiplexer and demultiplexer using inexpensive, discrete filters mounted on molded, optical blocks for both single-mode or multi-mode fiber optic communication systems wherein cross-talk between adjacent filters is reduced.
A further object of the invention is to provide an optical multiplexer/demultiplexer having preformed parts with premolded, passively aligned optics and a series of discrete filters and reduced cross-talk between filters.
Other objects and advantages of the invention will become apparent from the following description and drawings wherein: